Recreational vehicles enjoy widespread popularity because they enable their owners to travel away from home for extended periods while enjoying many of the comforts of home. One present limitation of such recreational vehicles is that their interior spaces are somewhat small and cramped compared to a normal living space. While many factors contribute to this design limitation, the major contributor is the relatively narrow width of the normal street or highway. The need to travel within the confines of a normal highway traffic lane sets an upper limit on the feasible width of a recreational vehicle. Because this upper width limit is much smaller than the width of even a small room in a normal house, the interior of the recreational vehicle seems cramped by familiar comparison.
One ingenious solution to this problem is the hydraulically actuated expandable room which may be incorporated into a recreational vehicle such as a motor home or a travel trailer. The expandable room forms the interior space of the recreational vehicle in two telescoping sections. As shown schematically in FIG. 1 of the accompanying drawings, a trailer 10 includes a fixed portion 12 which is fixedly attached to a trailer frame 14, as is trailer axle 16. The trailer 10 further includes an expandable portion 18 which is slidingly engaged with the trailer frame 14 and configured so as to move in telescoping engagement with the fixed portion 12. The trailer 10 is illustrated in its retracted position in FIG. 1, in which the expandable portion 18 is telescopically nested within the fixed portion 12. In this retracted position, the trailer 10 is sufficiently narrow to travel within the confines of a normal highway traffic lane.
Referring now to FIG. 2, when the trailer 10 has been parked and is no longer restricted to the width of a normal highway traffic lane, expandable portion 18 may be telescopic, ally un-nested from fixed portion 12, such that the interior volume of the trailer 10 is substantially greater, approaching double the volume of the trailer 10 in its retracted position. Movement of the expandable portion 18 out of and into the fixed portion 12 is normally facilitated by a plurality of hydraulic cylinders (not shown) each having one end coupled to the fixed portion 12 and another end coupled to the expandable portion 18. Fixed portion 12 includes an integral roof 13 and expandable portion 18 includes an integral roof 19. The trailer 10 is therefore enclosed whether it is in its retracted or expanded position.
Fixed portion 12 and expandable portion 18 are supported in sliding engagement by a plurality of telescoping beams. Referring to FIG. 3, an example of such sliding engagement is provided by an expansion box beam 20 which slides in telescopic arrangement with fixed box beam 22. The desired spacing between the box beams 20 and 22 is maintained by a plurality of nylon shims (not shown) mounted on the interior surface of fixed box beam 22. Fixed box beam 22 is fixedly attached to a chassis mainrail 24 of the trailer frame 14. Fixed portion 12 is also coupled to the chassis mainrail 24. The distal end of expansion box beam 20 includes a mounting flange 26. The expandable portion 18 is fixedly attached to the mounting flange 26. When the hydraulic cylinders operate to cause relative motion between the fixed portion 12 and the expandable portion 18, telescopic movement of the box beams 20 and 22 occurs.
When the trailer 10 is in a retracted position, it is important to insure that the trailer is not inadvertently expanded. Likewise, when the trailer 10 is in an expanded position, it is important to insure that the trailer is not inadvertently retracted. For this reason, fixed box beam 22 includes a hole 28 drilled therethrough, while expansion box beam 20 includes holes 30 and 32 drilled therethrough. The holes 28-32 are positioned such that the holes 28 and 30 align when the trailer is expanded, and the holes 28 and 32 align when the trailer is retracted. Once the trailer has been moved to either position, a pin 34 (see FIG. 4) is placed through the two aligned holes, thereby preventing further relative movement of the fixed portion 12 and the expandable portion 18.
Such a locking arrangement, however, exhibits several problems in practice. First, it is difficult to align the two holes during hydraulic movement of the expandable portion 18. If the two holes are not aligned, the pin 34 cannot be inserted therethrough. Furthermore, such trailers have a tendency to warp over time, contributing to the difficulty in aligning the holes. An attempt has been made in the prior art to solve this problem by making the holes 30 and 32 larger than the hole 28, thereby eliminating the need for exact alignment. Drilling large holes in the expansion box beam 20, however, is undesirable. The larger the holes 30 and 32, the greater the compromise to the structural integrity of the expansion box beam 20.
A further problem encountered by the use of large holes 30 and 32 is illustrated in FIG. 4. When the locking pin 34 is engaged through the hole 30, 32, and there is relative movement between the fixed box beam 22 and the expansion box beam 20, the pin 34 strikes the hole 30, 32 at a very small area, resulting in a very large force per unit area transferred to the expansion box beam 20. Because the box beam. 20 is normally made from a relatively soft metal, severe deformation of the hole 30, 32 can occur over time, causing improper alignment of the fixed portion 12 to the, expandable portion 18, and further weakening the box beam 20.
There is therefore a need in the prior art for a device that will lock the fixed and expansion box beams at desired locations without exhibiting the problems of the prior art locking mechanisms. The present invention is directed toward meeting this need.